1. Field of the Invention
The present invention relates to an apparatus for reproducing a signal from a number of tracks formed on a recording medium and, more particularly, to tracking control for use in the apparatus.
2. Description of the Related Art
Two types of reproduction tracking systems for domestic-use video tape recorders (VTRs) have heretofore been proposed and put into practice. One type of reproduction tracking system is a dedicated control track system (CTL system) which is arranged to record a vertical synchronizing signal separated from a recorded signal on a tape in the longitudinal direction thereof by means of a fixed, magnetic head which is provided at a location on a tape path. The other type of reproduction tracking system is a system (4fATF system) in which four kinds of pilot signals having different, comparatively low frequencies are cyclically recorded in a multiplexed manner on a track on which a main signal is recorded. In such a 4fATF system, during reproduction, crosstalk components reproduced from both tracks adjacent to a track from which a main signal is reproduced are compared with each other to obtain a tracking error signal (ATF error signal).
However, the CTL system is disadvantageous to a reduction in the size of the entire assembly since a space for the fixed head is needed. In contrast, the 4fATF system is advantageous to a reduction in the size of the entire assembly, but the four kinds of pilot signals are needed.
In recent years, the digitization of domestic-use VTRs has proceeded and the image quality thereof has increasingly been improved. In such a situation, VTRs which are arranged to record an image signal for one field on a plurality of tracks in divided form have been developed so that a comparatively large amount of information can be recorded or reproduced, and tracking systems for use in such VTRs have been considered.
One example of such a tracking system will be described below in brief.
As is known, general VTRs are arranged to form a number of helical tracks and record a video signal on each of the helical tracks. In this tracking system, pilot signals are multiplexed on the video signal every other track. More specifically, two kinds of pilot signals f1 and f2 having different frequencies are alternately recorded in units of one track; that is to say, each of the pilot signals f1 and f2 is multiplexed periodically at intervals of four tracks.
During reproduction, when a reproducing head reproduces a main signal from a track on which no pilot signal is multiplexed, crosstalk components of the pilot signals f1 and f2 derived from both tracks adjacent to that track are picked up from the output of the reproducing head, and the crosstalk components are compared with each other. A tracking error signal (ATF error signal) is obtained from the result of this comparison.
The aforesaid pilot signals may be multiplexed in such a way that an analog pilot signal is simply multiplexed onto a digital video signal. As another approach, the method of controlling modulation to add a pilot signal as a frequency component of a digital modulated signal has been proposed.
The above brief description has been made in connection with the arrangement of the VTR system and the tracking system on both of which preferred embodiments of the present invention to be described later are based. The present tracking system is hereinafter referred to as the "2fATF system".
According to the above-described 2fATF system, a pilot-signal generating rotation and the recording or reproduction of frames are synchronized with each other in units of two frames (twenty tracks) in the case of a VTR which is arranged to record one frame on ten tracks. For this reason, owing to a reversal of the positional order of the tracks on which the pilot signals f1 and f2 are respectively recorded, if reproduction is started from an odd frame, a head for a channel 1 reproduces f2+f1 as a crosstalk component, while a head for a channel 3 reproduces f1+f2 as a crosstalk component, and, if reproduction is started from an even frame, the head for the channel 1 reproduces f1+f2 as a crosstalk component, while the head for the channel 3 reproduces f2+f1 as a crosstalk component. Accordingly, if a logic for an ATF error signal is selected in synchronism with a head switching signal, the logic for the ATF error signal for coping with a track deviation is inverted when reproduction is started from an even frame. As a result, even if tracking deviates, tracking control will be executed so that the tracking is deviated to a further extent.
One approach to the tracking deviation is to execute recording by necessarily starting a recording from an odd frame and completing the recording on an even frame and to execute reproduction by necessarily starting a reproduction from an odd frame and completing the reproduction on an even frame. However, this approach is not practical, since all operating modes, such as recording and reproduction, must be performed in units of two frames.